1. Field of the Invention
The present invention relates to a novel construction for an internal combustion engine used in an automotive vehicle and, more particularly, to an in-line internal combustion engine having a novel intake structure. The invention relates specifically to an-in-line internal combustion engine whose cylinders are arrayed in a common straight line as opposed to a V-type internal combustion engine whose cylinders are arrayed in two inclined rows and form a V-shape.
2. Description of the Prior Art
An internal combustion engine is known which has a surge tank of relatively large volume. Because the surge tank has a large volume, it is usually located above the engine body. Recently, an in-line engine has been developed with improved charging efficiency obtained by means of dynamic effects, such as, inertial effects. The engine is designed such that the surge tank is connected by discrete intake tubes to a plurality of cylinders disposed in the engine body. For this engine, making the discrete intake tubes as long as possible is desirable in order to achieve optimum dynamic effects for the range of predetermined engine speed. When long intake tubes are used, it is important to arrange them compactly in the space afforded or provided for the engine in the automobile.
Japanese Utility Model Publication No. 59(1984)-165562 discloses an arrangement wherein a surge tank is located above an engine body, and discrete intake tubes connect intake ports formed in a engine body to the surge tank. The intake tubes are formed in a curved shape. More specifically, the discrete intake tubes are designed to extend from one side of the engine body, in a direction away from the engine body, and then to curve upwardly in a U-shaped manner toward the surge tank where they are connected.
However, such an arrangement for an in-line engine is inherently unable to withstand, absorb or dissipate vibration in a satisfactory manner. Such an intake structure connected to the surge tank and throttle body is subject to unwarranted vibration during the engine operation due to the heavy weight of the surge tank and the throttle body. The vibration occurs mainly in a vertical plane parallel to the axis of cylinders. It was thought that one way of suppressing these unwanted vibrations would be to make the wall thickness of the intake tubes greater, the idea being to enhance the stiffness of the intake tubes. Increasing the wall thickness, however, only serves to increase the weight of the intake tubes, and the result is unacceptable.